1. Field of the Invention
The present invention relates to a simple, low cost and highly reliable apparatus for indicating peak pressures encountered in high pressure applications, such as within the cartridges exploded in gun barrels during the firing of high caliber guns.
2. Description of the Prior Art
In the recent past a number of failure incidents involving large caliber guns have taken place during ballistics testing by the U.S. Army. In these cases, no accurate data of the pressures reached in the gun before tube failure were obtained, this occurred in spite of the presence of both mechanical pressure gases and piezoelectric transducers on the gun. It was apparent in these failures that the gages used had neither the range to measure the high chamber pressure nor the capacity to survive the shock and impact damages associated with a catastrophic event. The upper range of the crusher gage was 110,000 psi and the upper range of the piezoelectric gage was 108,000 psi. The crusher gage relies on fine dimensional measurements on a copper sphere for its pressure reading. This gage comprises a housing with a cylinder therein and a piston in the cylinder. A sphere of copper is placed between the flat end of the piston and the flat end of the cylinder. Pressure against the piston crushes this sphere of copper in proportion to the force exerted against the piston.
The crusher gage may be inaccurate and inconsistent in successive readings for several reasons. The crusher gage relies on a moving piston to apply pressure to the sphere. If the free movement of the piston is hindered, the gage will not accurately record pressures. Free movement of the piston becomes difficult to achieve at temperature extremes (below -40.degree. C. and above 60.degree. C.) and at pressure extremes (over 110,000 psi), since body parts expand nonuniformly under temperature and deform excessively under pressure eliminating built-in tolerances.
The piezoelectric gage, on the other hand, is even more easily incapacitated by the destruction of wires and terminal connections. In addition, its piezo crystal may respond unpredictably if the hole into which it is fitted becomes deformed.
A third kind of high pressure indicator or gage is described in U.S. Pat. No. 3,345,876 wherein a circular disc is placed within a high pressure gage. The disk is subjected to a high pressure which causes the disc to deform. The disc is then examined to determine the degree of pressure reached by the amount of deformity of the disc. However, the pressure gage described in the above mentioned patent is only reliable for peak pressures of 10,000 to 100,000 psi.
A new gage has been designed to address the need for measurement of chamber pressure above the range of the pressure gage and other gages mentioned above, although pressures above 120,000 psi are presently outside the range of normal functioning guns.